Is your NSX failing smog? Read this.

[darock]

I had issues with the emission test last week.

Car was running a little rich. Did not reach lambda 1 and therefore also not got below 80ppm HC.

I have the fuel pump resistor bypassed because the fuel pump is a bit week after about 170k miles. I think this is the reason for that. The fuel pressure is a bit too high at idle.
Unfortunatelly I did not have time to test it with the resistor connected.

IAT cleaned
Injectors freshly cleaned
Air filter clean
Throttle body cleaned and idle adjusted
New 300cell highflow cats
New Denso O2 sensors

anyone had that issue as well?

I read on here somewhere that the bypassed resistor might make the engine run rich at lower engine speeds.

Bernhard

 

[SilverOne]

I have a friend that has a car without CAT, but wouldn't want to take it back to stock. Anyone know of place in SoCal that can help with smog?

 

[911TT]

Failed smog turned into a pass after a few easy steps

this post helped me a lot so I thought I'd share my experience as well.

I bought a 91 NSX in Colorado, the car is mostly stock except for a HKS Intake (will be changed by next smog with stock part) and Comptech headers.
I went to Patrick full of confidence everything would go well and here are the results

So after this miserable outcome and chatting with Patrick about ways to correct the issues plus reading through this very same post here are the few things I did:
Clean the AIT (it was very dirty and it is quite stained but I still decided to not buy a new one)
Pour a can of BG44K in the gas tank (filed in the tank the day before on my way to a canyon drive and emptied said tank )
Warm up the cats by running the car to 7-8000rpm several times on the highway before heading to the shop

Simple things leading to this result this morning

sure it barely passed but it still did and considering I did the absolute minimum I think it is reassuring.
Considering the readings I got from the first test I think it shows what little things can do. Another member posted similar numbers here (sorry I forgot the name) and his post gave me confidence. In all honesty when I headed over Patrick's shop this morning I was expecting a fail but I wanted to know how much of an improvement these easy steps would make. If it was significant enough I was going to buy a new AIT, change oil and spark plugs and try again. Luckily I didn't have to and this is a wonderful way to start 2017, I am a very happy camper !

I wish you all the best for 2017, get out there and drive your amazing cars.

 

[MCM]

Look at my max in July and yours in Jan. Houston, we have a problem.
695 / 549........ 717 / 507
Or maybe I just don't understand it and someone can explain it to me.
How and why it keeps changing.
Thanks

 

[911TT]

Look at my max in July and yours in Jan. Houston, we have a problem.
695 / 549........ 717 / 507
Or maybe I just don't understand it and someone can explain it to me.
How and why it keeps changing.
Thanks

indeed, I didn't even pay attention...at this rate it will indeed become absolutely impossible to pass.

 

[911TT]

on another note, love your garage, E30 M3 and NSX. A friend of mine has an M3, hopefully I'll get a chance to experience this special machine very soon

 

[nsxvtecvtec]

my 91 just failed due to higher NO than the limit

 

[8R6]

just adding another data point to this thread. got the car smogged today and other than the HC being right at the max limit, the NOx and CO tests passed! i did drive for a little over an hour (half of it being in heavy traffic) and luckily towards the end the fwy's and roads were open so i wrung it out a few times to get the cats hot. idled for probably about 10 min or less and then right on to the rollers for the test.

95 5-spd with only mods being headers and exhaust. everything else stock.

View attachment 142470

 

[taqman15]

Here are the results of my smog test(s).

Initial test was showing high NOX(barely passing the 25mph):



Since I hadn't driven the car much, I thought just adding some fuel additive would work. Got some Rislone Fuel Treatment and burned a tank of gas:



You can see the one NOX values improved but the other got worse. So thought it may be the cats. Borrowed a set from a friend and headed back to re-test:



Not only did the cats not help, all the values got WORSE. Reading this thread, I did a quick cleaning of the IAT sensor and went back the same day:



So now I got the 15mph to barely pass. The tech suggested its an EGR issue. I went home and read up on it and everything I read said the EGR shouldn't be the issue. He said he can only run in 2nd or 3rd gear too. Thought about putting smaller tires on the rear to create a better load and higher rpm but decided not to yet. Not having many options, I went ahead and bought a brand new OEM EGR and crossed my fingers:



Finally was able to pass. It only took 5 trips to the smog shop I made sure I got the cats nice and hot with a long 40 mile drive and kept the car running while I was filling out paperwork.

 

[MCM]

Keeping the old thread alive. Easy pass when the EGR valve is open.
Hard part? Running the test hot enough, at low rpm's and getting it to open.
Also the new fuel tank EVAP test is a real joy. $45.00 to see if my tank leaks, Nuts.
Passed the smog ck. Only $134.95 ck=81.70, Cert = $8.25, Evap test = $45.00
Was a bit pricey, but got it done in one trip.
What a State Rip off. But thanks again to Ronnie at Irvine auto, passed using one year old gas
after sitting for months and months. Sad to say, only 200 miles driven in 2 years. 60 of those was getting it smogged. LOL LOL
For the record:

 

[lithiumus]

Im baaaack...

So after the last pass about 4 years ago (we have to pass every 2 years in Ontario Canada) it failed again. Looking at my previous pass, it definitely looks like I have an issue somewhere...

Im failing with high HC at idle only and when I passed last time, it was pretty high but under the limit (170). This time im well over it. Time to do some diagnostics... as you can see, all the other numbers look fantastic.

The caveat is that I was using 6 month old gas...

Sent from my iPhone using Tapatalk

 

[Old Guy]

Do check the manifold air temperature sensor to make sure its clean. If the sensor is dirty and reading low, the air density correction for the ECU will be off typically causing a low AFR and making life harder for the cat and requiring more EGO correction. Even if it doesn't fix the problem, its a no cost check and if it is dirty just a few $ for a can of cleaner.

 

[lithiumus]

Do check the manifold air temperature sensor to make sure its clean. If the sensor is dirty and reading low, the air density correction for the ECU will be off typically causing a low AFR and making life harder for the cat and requiring more EGO correction. Even if it doesn't fix the problem, its a no cost check and if it is dirty just a few $ for a can of cleaner.

Thanks Old Guy. Ill definitely check it. I actually replaced it 4 years ago but doesnt hurt to clean it up.

Ive burned off all the old fuel and put in a fresh tank of gas. I put some injector cleaner in the fuel and ill burn off another tank.

Will also clean the air filter, put some new plugs in, check the PVC and other vacuum hoses. Im very suspicious about the vacuum as I dont notice much change when i pull a hose out etc. Could be a leak i dont know about but there arent that many hoses and ive checked them many times before but worth another look...

BTW, I already notice a difference in the idle with the fresh fuel. Its not as rough and noticeably smoother. Obviously not perfectly smooth but after a day of fuel burn and driving, I filled up at the end of the day and i could tell the difference.


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[MCM]

taqman15 / I know its been a year.......... I did the same thing. Replaced the EGR valve but believe it was unnecessary.
It seems it only gets the signal to open when everything is very hot. Like running the car for 40 minutes and not letting it cool down at all prior to the test.
Wish I had a toggle switch to open the egr during the test. lol lol
I think people pay a lot of money for new parts etc due to this issue. Again, wish I knew more about it.
Hopefully the current administration gets rid of CARB all together. And goes back to federal regulations.
The ones the cars were designed to meet in the 1st place.
Wouldn't that be nice..............

 

[nis350]

is the EVAP test new for 2018?

I recalled part of the test for the older cars was pumping some sort of gas into the gas tank, but they've been doing that for quite a few years now.

Keeping the old thread alive. Easy pass when the EGR valve is open.
Hard part? Running the test hot enough, at low rpm's and getting it to open.
Also the new fuel tank EVAP test is a real joy. $45.00 to see if my tank leaks

 

[MCM]

Your probably right. I may have been confused by the guys brand new evap machine, and high price to have it used on my car.
He mentioned it was a new test? That I might not have had before? But am not sure.......
No complaints though. Made it in one trip. Yrs ago I used to have to make several trips to different shops. And pay each time.
And if it failed, they would just say "Fix it and come back"........Without knowing what to fix.
I bet I have been told to replace the cats 5 times in the past from test stations that had no idea why the car failed.
Seems to be the standard answer from a tester. Even if the car only has 65k miles.

 

[8R6]

sad to say, only 200 miles driven in 2 years. 60 of those was getting it smogged. Lol lol

haahhahaha

 

[Fabiodaddy]

This is a good tip. My 91 failed emissions for the first time ever (as long as I've owned it anyway). Everything passed except idle HC. Our limit is 220 here in Utah and I blew a 358 on idle HC test. 2500 rpm was fine as was everything else. Just idle HC. The car recently got new air cleaner, plugs, valve adjustment and timing etc. It is well sorted currently. So pulled the IAT and sure enough it was carboned up and a bit oily. I cleaned it with carb cleaner and dumped some injector cleaner in the car for good measure and went for a drive to get it good and warm. I went in for my retest and guess what.....idle HC was down to 46 (from 358) and everything else still passed with very low numbers. So easy fix and a good one. Thanks guys.

 

[biggrumble]

I recently "inherited" my father's NSX and it just barely failed CA smog (high HC at 15mph in 2nd gear). My dad had had the Comptech Supercharger installed shortly before he passed. I was going to try cleaning the AIT sensor and trying again, but when I looked under the rear hood I couldn't see where it was located based on the diagram in the parts guide. Is the sensor in a different place when the CTSC is installed, or do I just need to look harder? Thanks!

 

[biggrumble]

The car (a 1992) is just barely failing, running rich. I chatted with Shad at Driving Ambition (the guy who installed the CTSC supercharger right before my dad passed) and he recommended driving it hard before bringing it in; I tried, but apparently that didn't do quite enough. When I talked to Don at Hilltop, he wouldn't commit to recommending anything, but said that the O2 sensors were the a good first bet and failing that trying to go back to the stock headers (expensive!). Do you guys have any other suggestions?

 

[MCM]

Go here and report back to us...

This might make a good sticky for 91-94's.

After 12 yrs of ownership in Ca. ....... Finally figured it out. (Ronnie at Irvine auto repair actually)
Highly recommended if you live in the area you get your NSX smog there. 91-94 specifically.
My cars issue was a lazy EGR valve. And its by design. For cold start ups.
Most 91-94 NSX's according to Ronnie have this issue. And it can drive you & the smog guys nuts.
Even after replacing my EGR valve 4 yrs ago It was still hit and miss.
The solution for me (And other NSX's he tests is to make sure the EGR valve is operating & open prior to running the test.
Past 1st time. Old gas, have not driven the car much over the past 2 yrs. (few hundred miles maybe)
No more driving the hell out of it getting it hot, silly $$ race gas, magic potions, new plugs, cats, replacing all sorts of things prior to getting a smog test.
Mystery solved. For me anyway. Just give Ronnie a call if you need more details.

 

[biggrumble]

I would definitely go there if I was in Socal, although I'm up in the Bay Area so it'd be a 6 hour one way drive for me in the best case scenario. I tried going to Don at Hilltop in Daly City, and he was a bit more cryptic in his suggestions than I would have liked, "You could try replacing the oxygen sensors or going back to stock headers, but you have to do your own research." Other shops I've called around have just told me to try driving it again since it didn't fail by much, although if it was a 1991 car it would have failed both HC tests and the NOx 15mph test (thanks California?).

 

[MCM]

Find a smog shop that can "make sure the EGR valve is operating & open prior to running the test"

 

[biggrumble]

Well, after talking to a few NSX shops they generally recommended trying to drive the car harder before getting it smogged. I changed the oil+filter, air filter, added some octane booster (in the hope of "persuading" the ECU to run a little leaner), took it on a highway cruise in 2nd gear before trying again and managed to pass by the skin of my teeth!



I would have tried the AIT sensor cleaning trick, but it looks like the CTSC manifold covers that up, and so getting to it seemed way above my pay grade. I should just smile and enjoy the car for now, but I'm wondering what I'm going to do in a year and half when I try again (at which point I'm sure the emissions regulations will be stricter). Given how high the CO2 and how low the CO out was, it seems like the cats are working fine but they might get overwhelmed over time by the car running rich. I should probably hold onto the oxygen sensors I picked up and get a fuel system cleaning done.

 

[Mark Henderson]

I have '94 with CTSC, Comptech headers and cat-back, original cats. Have passed CA smog every time in the past, including 2013, 2015, 2017 with the CTSC. But I was bumping the numbers (particularly NOx) and hadn't driven the car much lately - although it was running great. My 2019 reg said I had to do the more stringent (?) STAR smog. Long story short, the car passed with flying colors and plenty of margin - here's what I did (and big endorsements):

- Took the car to Ramon at Niguel Motors for his attention. Asked him to do whatever he would do to pass smog. He had installed the CTSC and other bits 7 years ago, and I'd not added a lot of miles. So he had changed the IAT/AIT and generally cleaned things up back then. This time he did oil filter/change, air filter (didn't like my filthy K&N hahahah) and that was about it (other than a rear shock change out). He turned the car FAST, his bill was typically reasonable and we enjoyed some NSX war stories. Money VERY well spent, and not a lot of money. Thank you Ramon!
- Went to Ronnie at Irvine Auto. Everything you see in this thread is spot on - Ronnie knows these cars, he knows what he's doing, and he has clean shop! The EGR seems to be the trick, and he takes the time to get that thang open. Passed with plenty of margin - the car runs REALLY clean!!! And also a really reasonable cost. Thank you Ronnie!

None of this should be news to SoCal NSXen - Ramon and Ronnie are surely well known around these parts. Thank you, gentlemen, for keeping these old (!) cars running in tip-top shape!!! Highly recommended. Go see these guys, you'll be taken care of. I'll be back!